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DETERMINATION OF CONDITION CATEGORIES FOR BIOTIC INDICES USING POWER ANALYSIS
Citation:
Blocksom, K A. AND F A. Fulk. DETERMINATION OF CONDITION CATEGORIES FOR BIOTIC INDICES USING POWER ANALYSIS. Presented at North American Benthological Society, La Crosse, WI, June 3-8, 2001.
Impact/Purpose:
The goal of this research is to develop methods and indicators that are useful for evaluating the condition of aquatic communities, for assessing the restoration of aquatic communities in response to mitigation and best management practices, and for determining the exposure of aquatic communities to different classes of stressors (i.e., pesticides, sedimentation, habitat alteration).
Description:
Multimetric biotic indices are often used in bioassessment programs to determine the condition of water resources. These indices are typically divided into a number of condition tiers (e.g., good, poor). However, the number of tiers is often based on professional judgement. We used bootstrapping and Monte Carlo methods of power analysis to establish and compare the number of condition tiers defensible for a newly developed biotic index for the Mid-Atlantic highlands. Through power analysis, we calculated the effect size, the minimum difference in index scores necessary to correctly recognize that any two sites differ in condition. Dividing the range of the index by the effect of power anaysis, we calculated this effect size based on the empirical distribution of the data and required replicated samples. The Monte Carlo method relied on an assumed distribution and an estimate of variability to ascertain the effect size. Results from the Monte Carlo method were sensitive to both the estimate of variability and the sample size. However, this sensitivity decreased beyond a sample size of two per site.